Gnuplot: Plot x2 axis with respect to x1 axis

Question

I seem to be having some difficulty finding the answer to this question online. The title is the basic question, but to be more specific I would like to have two x axes, one

Answer 1

The best way: Plot your data as usual on the x1 and y1 axes, but place additional labels on the x2-axis with x2tic(column_number):

set x2tics
set xtics nomirror
plot 'data.txt' using 3:2:x2tic(1) w lp

see: Plot y1 in x1 with respect to x2 axis